The present invention relates to filters, and, more particularly, to filters for filtering combustion gases generated in a pyrotechnic inflatable passenger restraint system for a motor vehicle.
Concerns with passenger safety in motor vehicles have led to the development of inflatable vehicle occupant safety systems. One example of such a system is the vehicle “airbag”, a passive restraint and protection system comprising a bag or pillow-like bladder that is inflated in an extremely short period of time using compressed or chemically-generated gas to fill the bag. The inflated bag is disposed or deployed between the front or side of the passenger and an interior portion of the vehicle's passenger compartment.
In current airbag designs, the gas generated escapes a combustion chamber and is propelled towards the airbag, so that the gases and any particulates would impinge on the bag itself if no filter were present. If no measures are taken to ameliorate the degradative effects of the combustion gases, the gases and/or particulates may penetrate the bag, potentially causing failure of the bag and possible injury to a passenger. Consequently, current airbag inflators often contain a filter for filtration of solids and cooling of combustion gases. Current filtering devices may comprise layers of metal screens of various mesh sizes and one or more layers of a non-combustible fibrous material packed between the screens. The efficiency of this type of filter is dependent upon how tightly the material is packed; a tighter packing leads to more efficient filtering but also to a higher pressure drop. There is also a problem with quality control in the mass fabrication of such screen-mat composites with respect to ensuring a uniform pressure drop across any given filter.
Yet another problem in designing inflator filtration devices is that, as the filter becomes clogged, the pressure drop across the filter increases. Accordingly, the mechanical stresses on the filter are increased, and combustion gases and particulates move through the filter at a higher velocity, necessitating improved filter strength and toughness to withstand the higher flow rate, pressure drop, and particulate velocity into the filter. The filter must be positionally stabilized against the effects of such stresses.